Phosphor materials and related devices

ABSTRACT

A phosphor material is presented that includes a blend of a first phosphor, a second phosphor and a third phosphor. The first phosphor includes a composition having a general formula of RE 2−y M 1+y A 2−y Sc y Si n-w Ge w O 12+δ :Ce 3+  wherein RE is selected from a lanthanide ion or Y 3+ , where M is selected from Mg, Ca, Sr or Ba, A is selected from Mg or Zn and where 0≦y≦2, 2.5≦n≦3.5, 0≦w≦1, and −1.5≦δ≦1.5. The second phosphor includes a complex fluoride doped with manganese (Mn 4+ ), and the third phosphor include a phosphor composition having an emission peak in a range from about 520 nanometers to about 680 nanometers. A lighting apparatus including such a phosphor material is also presented. The light apparatus includes a light source in addition to the phosphor material.

BACKGROUND

The invention relates generally to phosphor blends for wavelengthconversion, and specifically phosphor blends for the conversion ofradiation emitted by a light source. More particularly, the inventionrelates to phosphor blends for use with the blue light emitting diodes(LEDs).

A phosphor is a luminescent material that absorbs radiation energy in aportion of the electromagnetic spectrum and emits radiation energy inanother portion of the electromagnetic spectrum. One important class ofphosphors includes crystalline inorganic compounds of very high chemicalpurity and of controlled composition to which small quantities of otherelements (called “activators”) have been added to convert them intoefficient fluorescent materials. With the right combination ofactivators and inorganic compounds, the color of the emission can becontrolled. Most useful and well-known phosphors emit radiation (alsoreferred to as light herein) in the visible portion of theelectromagnetic spectrum in response to excitation by electromagneticradiation outside the visible range. For example, the phosphors havebeen used in mercury vapor discharge lamps to convert the ultra-violet(UV) radiation emitted by the excited mercury to visible radiation.Further, the phosphors may be used in a light emitting diode (LED) togenerate colored emissions that may generally not be obtained from theLED itself.

Light emitting diodes (LEDs) are semiconductor light emitters often usedas a replacement for other light sources, such as incandescent lamps.They are particularly useful as display lights, warning lights andindicating lights or in other applications where a colored light isdesired. The color of light produced by an LED is dependent on the typeof the semiconductor material used in its manufacture. The colored LEDsare often used in toys, indicator lights and other devices.

The colored semiconductor light emitting devices, including lightemitting diodes and lasers (both are generally referred to as LEDsherein), have been produced from Group III-V alloys such as galliumnitride (GaN). With reference to the GaN-based LEDs, light is generallyemitted in the UV and/or blue range of the electromagnetic spectrum.Until quite recently, the LEDs have not been suitable for lighting useswhere a bright white light is needed, due to the inherent color of thelight produced by the LEDs.

Techniques have been developed for converting the light emitted from theLEDs to useful light for illumination purposes. In one technique, theLED is coated or covered with a phosphor layer. The phosphor absorbsradiation generated by the LED, and generates radiation of a differentwavelength, for example, in the visible range of the spectrum.

A combination of LED generated light and phosphor generated light may beused to produce white light. The most popular white LEDs are based onblue emitting GaInN chips. The blue emitting LEDs are coated with aphosphor or a phosphor blend including red, green and blue emittingphosphors that converts some of the blue radiation to a complementarycolor, for example a yellow-green emission. The total of the light fromthe phosphor and the LED chip provides white light having a color pointwith corresponding color coordinates (x and y) and correlated colortemperature (CCT), and its spectral distribution provides a colorrendering capability, measured by the color rendering index (CRI).

These white LEDs typically produces white light with a CRI between about70 and about 80 for a tunable CCT greater than about 4000K. While suchwhite LEDs are suitable for some applications, it is desirable toproduce white light with higher CRIs (greater than about 90) and lowerCCT (less than 3000K) for many other applications.

Therefore, it would be desirable to provide new and improved phosphorblends that produce white light with high CRI and high lumen for lowCCT.

BRIEF DESCRIPTION

Briefly, most of the embodiments of the present invention provide aphosphor material that includes a blend of a first phosphor, a secondphosphor and a third phosphor. The first phosphor includes a compositionhaving a general formula ofRE_(2−y)M_(1+y)A_(2−y)Sc_(y)Si_(n-w)Ge_(w)O_(12+δ):Ce³⁺, wherein REcomprises a lanthanide ion or Y³⁺, M comprises Mg, Ca, Sr or Ba, Acomprises Mg or Zn; and 0≦y≦2, 2.5≦n≦3.5, 0≦w≦1, and −1.5≦δ≦1.5. Thesecond phosphor includes a complex fluoride doped with manganese (Mn⁴⁺),and the third phosphor include a phosphor composition having an emissionpeak in a range from about 520 nanometers (nm) to about 680 nanometers(nm).

Some embodiments relate to a lighting apparatus. The lighting apparatusincludes a light source; and a phosphor material radiationally coupledto the light source. The phosphor material includes a blend of a firstphosphor, a second phosphor and a third phosphor. The first phosphorincludes a composition having a general formula ofRE_(2−y)M_(1+y)A_(2−y)Sc_(y)Si_(n-w)Ge_(w)O_(12+δ):Ce³⁺, wherein REcomprises a lanthanide ion or Y³⁺, M comprises Mg, Ca, Sr or Ba, Acomprises Mg or Zn; and 0≦y≦2, 2.5≦n≦3.5, 0≦w≦1, and −1.5≦δ≦1.5. Thesecond phosphor includes a complex fluoride doped with manganese (Mn⁴⁺),and the third phosphor include a phosphor composition having an emissionpeak in a range from about 520 nm to about 680 nm.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic cross sectional view of a lighting apparatusaccording to one embodiment of the invention;

FIG. 2 is a schematic cross sectional view of a lighting apparatusaccording to one embodiment of the invention;

FIG. 3 is a schematic cross sectional view of a lighting apparatusaccording to one embodiment of the invention;

FIG. 4 is a schematic cross sectional view of a lighting apparatusaccording to one embodiment of the invention;

FIG. 5 is a schematic cross sectional view of a lighting apparatusaccording to one embodiment of the invention;

FIG. 6 shows the emission spectra of a phosphor blend using a 450 nmexcitation wavelength, in accordance with an exemplary embodiment of theinvention;

FIG. 7 shows the emission spectra of a phosphor blend using a 450 nmexcitation wavelength, in accordance with another exemplary embodimentof the invention;

DETAILED DESCRIPTION

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about,” is not limited to the precise valuespecified. In some instances, the approximating language may correspondto the precision of an instrument for measuring the value.

In the following specification and the claims that follow, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly dictates otherwise.

As used herein, the terms “may” and “may be” indicate a possibility ofan occurrence within a set of circumstances; a possession of a specifiedproperty, characteristic or function; and/or qualify another verb byexpressing one or more of an ability, capability, or possibilityassociated with the qualified verb. Accordingly, usage of “may” and “maybe” indicates that a modified term is apparently appropriate, capable,or suitable for an indicated capacity, function, or usage, while takinginto account that in some circumstances the modified term may sometimesnot be appropriate, capable, or suitable. For example, in somecircumstances, an event or capacity can be expected, while in othercircumstances the event or capacity cannot occur—this distinction iscaptured by the terms “may” and “may be”.

The terms “first,” “second,” and the like, herein do not denote anyorder, quantity, or importance, but rather are used to distinguish oneelement from another.

As used herein, the term “phosphor” or “phosphor material” or “phosphorcomposition” may be used to denote both a single phosphor composition aswell as a blend of two or more phosphor compositions. The phosphor blendmay contain blue, red, yellow, orange and green phosphors. The blue,red, yellow, orange and green phosphors are so called or known after thecolor of their light emission.

As used herein, the terms “substitution” and “doping” refer to adding anamount of an element in a material. Typically, an element in a materialis partially or fully replaced by another element on such addition. Itshould be noted that various phosphors described herein may be writtendown by enclosing different elements in parentheses and separated bycommas to show substitution or doping, such as in the case of((Ba,Ca,Sr)_(1−x)Eu_(x))₂Si₅N₈. As understood by those skilled in theart, this type of notation means that the phosphor can include any orall of those specified elements in the formulation in any ratio. Thatis, this type of notation for the above phosphor, for example, has thesame meaning as ((Ba_(a)Ca_(b)Sr_(1−a−b))_(1−x)Eu_(x))₂Si₅N₈, where aand b can vary from 0 to 1, including the values of 0 and 1.

Particular application is described, herein, in conjunction withconverting LED-generated ultraviolet (UV), violet, or blue radiationinto white light for general illumination purposes. It should beappreciated, however, that the invention is also applicable to theconversion of radiation from UV, violet and/or blue lasers as well asother light sources to white light.

Embodiments of the present techniques provide phosphor blends that maybe used in lighting systems to generate white light suitable for generalillumination and other purposes. The phosphor blends include a firstphosphor of general formula:RE_(2−y)M_(1−y)A_(2−y)Sc_(y)Si_(n-w)Ge_(w)O_(12+δ):Ce³⁺, wherein REcomprises a lanthanide ion or Y³⁺, M comprises Mg, Ca, Sr or Ba, Acomprises Mg or Zn; and 0≦y≦2, 2.5≦n≦3.5, 0≦w≦1, and −1.5≦δ≦1.5. In oneembodiment, the first phosphor may also be represented by generalformula of (RE_(1−x−z)Sc_(x)Ce_(z))₂M_(3−p)A_(p)Si_(n-w)Ge_(w)O_(12+δ),wherein RE comprises a lanthanide ion or Y³⁺, M comprises Mg, Ca, Sr orBa, A comprises Mg or Zn; and 0≦x<1, 0<z≦0.3, 0≦p≦2, 2.5≦n≦3.5, 0≦w≦1,and −1.5≦δ≦1.5. Advantageously, the phosphors made according to theseformulations may maintain high emission intensity (quantum efficiency)across a wide range of temperatures. The phosphors may be used inlighting systems, such as LEDs and fluorescent tubes, among others, toproduce blue and blue/green light.

In some embodiments, the first phosphor may have general formula of(Ca_(1−z)Ce_(z))₃Sc₂Si_(n-w)Ge_(w)O₁₂, where 0<z≦0.3. Specificembodiments of the first phosphor include the compositions where the Si,Ge component includes at least about 66% Si⁴⁺, at least about 83% Si⁴⁺,and 100% Si⁴⁺. Thus some specific embodiments include(Ca_(1−z)Ce_(z))₃Sc₂(Si_(1−c)Ge_(c))₃O₁₂ where c is from 0.67 to 1.

These phosphors of above formula, have reduced quenching of theluminescence at high temperatures (thermal quenching) as compared tomany current phosphors, for example YAG:Ce. Accordingly, these phosphorsmaintain their emission intensity across a large range of temperatures,which may mitigate losses of intensity or lamp color shifts as thetemperature of a lighting system increases during use.

The phosphor blends, further include a second phosphor that is a redline emitter and a third phosphor that has a peak emission in a broadwavelength range from about 520 nm to about 680 nm. The second phosphormay be a complex fluoride that is a line emitter and generates redlight. Suitable examples include complex fluorides doped with Mn⁴⁺, forexample (Na, K, Rb, Cs, NH₄)₂[(Ti, Ge, Sn, Si, Zr, Hf)F₆]:Mn⁴⁺ and thelike. In certain instances, a complex fluoride doped with Mn⁴⁺ isK₂[SiF₆]:Mn⁴⁺ (“PFS”) used in some illustrative blend examples furtherbelow.

The third phosphor may include a phosphor composition having an emissionpeak in a range from about 520 nanometers (nm) to about 680 nm. Thethird phosphor is usually a yellow or a yellow-orange phosphor havingbroad emission range. Non-limiting examples of suitable third phosphorsmay include a garnet, a nitride, and an oxynitride. Table 1 shows someof such examples. Any combination having two or more members selectedfrom the group consisting of a garnet, a nitride, and an oxynitride mayalso be used.

In some embodiments, the third phosphor may be a garnet of generalformula (A, Ce)₃M_(5−a)O_(12−3/2a), wherein 0≦a≦0.5, A comprises Y, Gd,Tb, La, Sm, Pr, or Lu, and M comprises Sc, Al, or Ga. An example of suchgarnet is Y₃Al₅O₁₂:Ce³⁺ (YAG). This garnet YAG has an emission peak in abroad wavelength range from about 525 nm to about 645 nm.

In some embodiments, the third phosphor may be a nitride of generalformula (A, Eu)_(x)Si_(y)N_(z), wherein 2x+3y=4z, and A comprises Ba,Ca, Sr, or a combination thereof. The nitride may be further doped withcerium. Some embodiments include A₂Si₅N₈:Eu²⁺, wherein A comprises Ba,Ca, or Sr. In certain instances, the nitride is of formula ((Ba, Ca,Sr)_(1−a−b)Eu_(a)Ce_(b))₂Si₅N₈, where 0≦a≦1 and 0≦b≦1. These nitridesemit in broad wavelength range from about 575 nm to about 675 nm.

In some embodiments, the third phosphor may be an oxynitride phosphor ofgeneral formula A_(p)B_(q)O_(r)N_(s): R, where A comprises barium, Bcomprises silicon, and R comprises europium; and 2<p<6, 8<q<10, 0.1<r<6,10<s<15. In these instances, A may further comprises strontium, calcium,magnesium, or a combination thereof; B may further comprise aluminum,gallium, germanium, or a combination thereof; and R may further comprisecerium. In certain instances, the oxynitide phosphor is of formula (Ba,Ca, Sr, Mg)₄Si₉O_(r)N_(14.66−(2/3) r): Eu such that r is greater thanabout 1 and less than or equal to about 4. The emission peak of theseoxynitrides emit in wavelength range from about 545 nm to about 645 nm.

TABLE 1 Formulas of the third phosphor used in the phosphor blend NameFormula Garnet Y₃Al₅O₁₂:Ce³⁺ Nitride ((Ba, Ca,Sr)_(1−a−b)Eu_(a)Ce_(b))₂Si₅N₈, where 0 ≦ a ≦ 1 and 0 ≦ b ≦ 1 Oxynitride(Ba, Ca, Sr, Mg)₄Si₉O_(r)N_(14.66 − (2/3)r); where 1 < r < 4

Each of the general formulas listed herein is independent of every othergeneral formula listed. Specifically, x, y, z, and other variables thatmay be used as numeric placeholders in a formula are not related to anyusage of x, y, z and other variables that may be found in other formulasor compositions.

When the phosphor material includes a blend of two or more phosphors,the ratio of each of the individual phosphors in the phosphor blend mayvary, depending on the characteristics of the desired light output, forexample color temperature. The relative amounts of each phosphor in thephosphor blend can be described in terms of spectral weight. Thespectral weight is the relative amount that each phosphor contributes tothe overall emission spectrum of the device. The spectral weight amountsof all the individual phosphors and any residual bleed from the LEDsource should add up to 100%. In a preferred embodiment, each of theabove described phosphors in the blend will have a spectral weightranging from about 1 percent to about 70 percent.

The relative proportions of each phosphor in the phosphor blends may beadjusted, so that when their emissions are blended and employed in alighting device, there is produced visible light of predetermined ccxand ccy values on the CIE (International Commission on Illumination)chromaticity diagram. As stated, a white light is preferably produced.This white light may, for instance, possess a ccx value in the range ofabout 0.25 to about 0.55, and a ccy value in the range of about 0.25 toabout 0.55.

The phosphors used to make phosphor blends, may be produced by mixingpowders of the constituent compounds and then firing the mixture under areducing atmosphere. Typically, oxygen-containing compounds of therelevant metals are used. For example, the exemplary phosphor(Ca_(0.97)Ce_(0.03))₃Sc₂Si₃O₁₂, discussed further in the examples below,may be produced by mixing the appropriate amounts of oxygen-containingcompounds of calcium, cerium, scandium, and silicon, and then firing themixture under a reducing atmosphere. Silicon may also be provided viasilicic acid. After firing, the phosphor may be ball milled, orotherwise ground, to break up any conglomerates that may have formedduring the firing procedure. The grinding may be performed after allfiring steps are completed, or may be interspersed with additionalfiring steps.

Non-limiting examples of suitable oxygen-containing compounds includeoxides, hydroxides, alkoxides, carbonates, nitrates, silicates,citrates, oxalates, carboxylates, tartarates, stearates, nitrites,peroxides and combinations of these compounds. In embodiments containingcarboxylates, the carboxylates used may generally have from one to fivecarbon atoms, such as formates, ethanoates, proprionates, butyrates, andpentanoates, although carboxylates having larger numbers of carbon atomsmay be used. The individual phosphor compositions and a blend of thesephosphors may be synthesized by any known method, for example asdescribed in U.S. Pat. No. 7,094,362 B2.

Further, the first phosphors, the second phosphors and the thirdphosphors discussed above may be blended to form a phosphor blend. Forexample, phosphor blends may be made that contain the first phosphorhaving the general formula (Ca_(0.97)Ce_(0.03))₃Sc₂Si₃O₁₂, the secondphosphor having the general formula K₂[SiF₆]:Mn⁴⁺, and the thirdphosphor of general formula Y₃Al₅O₁₂:Ce³⁺ (YAG). An activator ion may beused in these phosphors to obtain the desired emission spectrum. As usedherein, the term “activator ion” refers to an ion (for example Ce³⁺)doped in a phosphor that forms luminescent center and is responsible forthe luminescence of the phosphor. Such ions may include ions of Pr, Sm,Eu, Tb, Dy, Tm, Er, Ho, Nd, Bi, Yb, Pb, Yb, Mn, Ag, Cu, or anycombinations thereof.

In addition to the synthesis procedures discussed above, many of thephosphors that may be used in the blends described herein may becommercially available. For example, the phosphor YAG, used in blendcalculations in presently disclosed phosphor blends, may be commerciallyavailable.

The phosphors listed above are not intended to be limiting. Any otherphosphors, commercial and non-commercial, that form non-reactive blendswith the phosphors of the present techniques may be used in blends andare to be considered to be within the scope of the present techniques.Furthermore, some additional phosphors may be used, e.g., those emittingthroughout the visible spectrum region, at wavelengths substantiallydifferent from those of the phosphors described herein. These additionalphosphors may be used in the blend to customize the white color of theresulting light, and to produce sources with improved light quality. Insome embodiments, an additional phosphor may be a phosphor of generalformula:((Sr_(1−z)M_(z))_(1−(x+w))A_(w)Ce_(x))₃(A_(1−y)Si_(y))O_(4+y+3(x−w))F_(1−y−3 (x−w));wherein 0<x≦0.10 and 0≦y0.5, 0≦z≦0.5, 0≦w≦x; A may include Li, Na, K,Rb, or a combination thereof; and M may include Ca, Ba, Mg, Zn, or acombination thereof.

One embodiment of the invention is directed to a lighting apparatus thatincludes a phosphor blend radiationally coupled to a light source. Asused herein, the term “radiationally coupled” means that the elementsare associated with each other so that at least part of the radiationemitted from one is transmitted to the other. A combination of the lightfrom the light source and the light from the phosphor blend may be usedto produce white light. For example, a white LED may be based on a blueemitting InGaN chip. The blue emitting chip may be coated with thephosphor blend to convert some of the blue radiation to a complementarycolor, e.g. a yellow-green emission.

Non-limiting examples of lighting apparatus or devices include devicesfor excitation by light-emitting diodes (LEDs), fluorescent lamps,cathode ray tubes, plasma display devices, liquid crystal displays(LCD's), UV excitation devices, such as in chromatic lamps, lamps forbacklighting liquid crystal systems, plasma screens, xenon excitationlamps, and UV excitation marking systems. These uses are meant to bemerely exemplary and not exhaustive.

The light emitted from the lighting apparatus may be characterized usingany number of standard measurements. This characterization may normalizethe data and make the comparison of light emitted by different lightingapparatus easier to determine. For example, the total of the light froma phosphor and from an LED chip provides a color point withcorresponding color coordinates (x and y) in the CIE 1931 chromaticitydiagram and correlated color temperature (CCT), and its spectraldistribution provides a color rendering capability, measured by thecolor rendering index (CRI). The CRI is commonly defined as a mean valuefor 8 standard color samples (R1-8), usually referred to as the generalColor Rendering Index, or Ra. A higher value for CRI produces a more“natural” appearance for illuminated objects. By definition, anincandescent light has a CRI of 100, while a typical compact fluorescentlight may have a CRI of about 82. Further, the luminosity, or apparentbrightness, of a source may also be determined from the spectrum of theemitted light. The luminosity is measured as lumens/W-opt, whichrepresents the number of lumens that 1 watt of light having a particularspectral distribution would represent. A higher lumens/W-opt valueindicates that a particular source would appear brighter to an observer.

As the light emitted from combined lighting apparatus components isgenerally additive, the final spectra of phosphor blends and/or lightingapparatus may be predicted. For example, the amount of light emittedfrom each phosphor in a blend may be proportional to the amount of thatphosphor within the blend. Accordingly, the emission spectrum resultingfrom the blend can be modeled, and the spectral properties, e.g., theCCT, the CRI, color axes (x and y), and 1 m/W-opt may be calculated fromthe predicted emission spectrum. Various blends that may be made usingthe phosphors described above are discussed in the examples below.

Referring to the figures now, FIG. 1 illustrates an exemplary LED basedlighting apparatus or lamp 10 that may incorporate the phosphor blendsof the present techniques. The LED based lighting apparatus 10 includesa semiconductor UV or visible light source, such as a light emittingdiode (LED) chip 12. Power leads 14 that are electrically attached tothe LED chip 12 provide the current that causes the LED chip 12 to emitradiation. The leads 14 may include thin wires supported on thickerpackage leads 16 or the leads may comprise self-supported electrodes andthe package lead may be omitted. The leads 14 provide current to the LEDchip 12 and thus cause the LED chip 12 to emit radiation.

The lamp 10 may include any semiconductor blue or UV light source thatis capable of producing white light when its emitted radiation isdirected onto the phosphor. In one embodiment, the semiconductor lightsource comprises a blue emitting LED doped with various impurities.Thus, the LED 12 may comprise a semiconductor diode based on anysuitable III-V, II-VI or IV-IV semiconductor layers and having anemission wavelength of about 380 to 550 nm. In particular, the LED maycontain at least one semiconductor layer comprising GaN, ZnSe or SiC.For example, the LED may comprise a nitride compound semiconductorrepresented by the formula In_(i)Ga_(j)Al_(k)N (where 0≦i; 0≦j; 0≦k andi+j+k=1) having an emission wavelength greater than about 380 nm andless than about 550 nm. Preferably, the chip is a near-UV or blueemitting LED having a peak emission wavelength from about 400 to about500 nm. Such LED semiconductors are known in the art. The light sourceas described herein is an LED for convenience. However, as used herein,the term is meant to encompass all semiconductor light sourcesincluding, e.g., semiconductor laser diodes.

In addition to inorganic semiconductors, the LED chip 12 may be replacedby an organic light emissive structure or other light sources. Othertypes of light sources may be used in place of LEDs, such as the gasdischarge device discussed with respect to FIG. 5, below. Examples ofgas discharge devices include low-, medium-, and high-pressure mercurygas discharge lamps.

The LED chip 12 may be encapsulated within a shell 18, which enclosesthe LED chip and an encapsulant material 20 (also referred to as“encapsulant”). The shell 18 may be glass or plastic. The encapsulant 20may be an epoxy, plastic, low temperature glass, polymer, thermoplastic,thermoset material, resin, silicone, silicone epoxy, or any other typeof LED encapsulating material. Further, the encapsulant 20 may be aspin-on glass or some other high index of refraction material.Typically, the encapsulant material 20 is an epoxy or a polymermaterial, such as silicone. The shell 18 and the encapsulant 20 aretransparent, that is substantially optically transmissive, with respectto the wavelength of light produced by the LED chip 12 and a phosphormaterial 22, such as the phosphor blends of the present techniques.However, if the LED chip 12 emits light that is within the UV spectrum,the encapsulant 20 may only be transparent to light from the phosphormaterial 22. The LED based lighting apparatus 10 may include anencapsulant 20 without an outer shell 18. In this application, the LEDchip 12 may be supported by the package leads 16, or by a pedestal (notshown) mounted to the package leads 16.

The phosphor material 22 is radiationally coupled to the LED chip 12. Inone embodiment, the phosphor material 22 may be deposited on the LEDchip 12 by any appropriate method. For example, a solvent basedsuspension of phosphors can be formed, and applied as a layer onto thesurface of the LED chip 12. In a contemplated embodiment, a siliconeslurry in which the phosphor particles are randomly suspended may beplaced over the LED chip 12. Thus, the phosphor material 22 may becoated over or directly on the light emitting surface of the LED chip 12by coating and drying the phosphor suspension over the LED chip 12. Asthe shell 18 and the encapsulant 20 will generally be transparent, anemitted light 24 from the LED chip 12 and the phosphor material 22 willbe transmitted through those elements. Although not intended to belimiting, in one embodiment, the median particle size of the phosphormaterial 22 as measured by light scattering may be from about 1 to about15 microns.

A second structure that may incorporate the phosphor blends of thepresent techniques is illustrated in the cross section of FIG. 2. Thestructure in FIG. 2 is similar to that of FIG. 1, except that thephosphor material 22 is interspersed within the encapsulant 20, insteadof being formed directly on the LED chip 12. The phosphor material 22may be interspersed within a single region of the encapsulant 20 orthroughout the entire volume of the encapsulant 20. Radiation 26 emittedby the LED chip 12 mixes with the light emitted by the phosphor material22, and the mixed light may be visible through the transparentencapsulant 20, appearing as emitted light 24.

The encapsulant 20 with the interspersed phosphor material 22 may beformed by any number of suitable plastics processing techniques. Forexample, the phosphor material 22 may be combined with a polymerprecursor, molded around the LED chip 12, and then cured to form thesolid encapsulant 20 with the interspersed phosphor material 22. Inanother technique, the phosphor material 22 may be blended into a moltenencapsulant 20, such as a polycarbonate, formed around the LED chip 12,and allowed to cool. Processing techniques for molding plastics that maybe used, such as injection molding, are known in the art.

FIG. 3 illustrates a cross section of a structure that may incorporatethe phosphor material 22 of the present techniques. The structure shownin FIG. 3 is similar to that of FIG. 1, except that the phosphormaterial 22 may be coated onto a surface of the shell 18, instead ofbeing formed over the LED chip 12. Generally, the phosphor material 22is coated on the inside surface of the shell 18, although the phosphormaterial 22 may be coated on the outside surface of the shell 18, ifdesired. The phosphor material 22 may be coated on the entire surface ofthe shell 18 or only a top portion of the surface of the shell 18. Theradiation 26 emitted by the LED chip 12 mixes with the light emitted bythe phosphor material 22, and the mixed light appears as emitted light24.

The structures discussed with respect to FIGS. 1-3 may be combined, withthe phosphor material located in any two or all three locations or inany other suitable location, such as separately from the shell orintegrated into the LED. Further, different phosphor blends may be usedin different parts of the structure.

In any of the above structures, the LED based lighting apparatus 10 mayalso include a plurality of particles (not shown) to scatter or diffusethe emitted light. These scattering particles would generally beembedded in the encapsulant 20. The scattering particles may include,for example, particles made from Al₂O₃ (alumina) or TiO₂. The scatteringparticles may effectively scatter the light emitted from the LED chip12, and are generally selected to have a negligible amount ofabsorption.

In addition to the structures above, the LED chip 12 may be mounted in areflective cup 28, as illustrated by the cross section shown in FIG. 4.The reflective cup 28 may be made from or coated with a reflectivematerial, such as alumina, titania, or other dielectric powder known inthe art. Generally, the reflective surface may be made from Al₂O₃. Theremainder of the structure of the LED based lighting apparatus 10 ofFIG. 4 is the same as that of the previous figure, and includes twoleads 16, a conducting wire 30 electrically connecting the LED chip 12with one of the leads 16, and an encapsulant 20. The reflective cup 28may conduct current to energize the LED chip 12, or a second conductingwire 32 may be used for the same. The phosphor material 22 may bedispersed throughout the encapsulant 20, as described above, or may bedispersed in a smaller transparent casing 34 formed within thereflective cup 28. Generally, the transparent casing 34 may be made fromthe same materials as the encapsulant 20. The use of the transparentcasing 34 within the encapsulant 20 may be advantageous in that asmaller amount of the phosphor material 22 may be required than if thephosphor were to be dispersed throughout the encapsulant 20. Theencapsulant 20 may contain particles (not shown) of a light scatteringmaterial, as previously described to diffuse the emitted light 24.

FIG. 5 is a perspective view of a lighting apparatus 36 based on a gasdischarge device, such as a fluorescent lamp, which may use the phosphorblends of the present techniques. The lamp 36 may include an evacuatedsealed housing 38, an excitation system 42 for generating UV radiationand located within the housing 38, and a phosphor material 22 disposedwithin the housing 38. End caps 40 are attached to either end of thehousing 38 to seal the housing 38.

In a typical fluorescent lamp, the phosphor material 22, such as thephosphor blends of the present techniques, may be disposed on an innersurface of the housing 38. The excitation system 42 for generating theUV radiation may include an electron generator 44 for generatinghigh-energy electrons and a fill gas 46 configured to absorb the energyof the high-energy electrons and emit UV light. For example, the fillgas 46 may include mercury vapor, which absorbs energy of thehigh-energy electrons and emits UV light. In addition to mercury vapor,the fill gas 46 may include a noble gas such as argon, krypton, and thelike. The electron generator 44 may be a filament of a metal having alow work function (for example, less than 4.5 eV), such as tungsten, ora filament coated with alkaline earth metal oxides. Pins 48 may beprovided to supply electrical power to the electron generator 44. Thefilament is coupled to a high-voltage source to generate electrons fromthe surface thereof.

The phosphor material 22 is radiationally coupled to the UV light fromthe excitation system 42. As previously described, radiationally coupledmeans that the phosphor material 22 is associated with the excitationsystem 42 so that radiation from the UV light from the excitation system42 is transmitted to the phosphor material 22. Thus, a phosphor materialthat is radiationally coupled to the excitation system 42 may absorbradiation, such as the UV light emitted by the excitation system 42,and, in response, emit longer wavelengths, such as blue, blue-green,green, yellow, or red light. The longer wavelength of light may bevisible as emitted light 24 transmitted through the housing 38. Thehousing 38 is generally made of a transparent material such as glass orquartz. Glass is commonly used as the housing 38 in fluorescent lamps,as the transmission spectrum of the glass may block a substantialportion of the “short wave” UV radiation, i.e., light having awavelength of less than about 300 nm.

A particulate material, such as TiO₂ or Al₂O₃, may be used inconjunction with the phosphor blend 22 to diffuse light generated by thelight source 36. Such a light scattering material may be included withthe phosphor blend 22 or separately disposed as a layer between theinner surface of the housing 38 and the phosphor blend 22. For afluorescent tube, it may be advantageous to have the median size of theparticles of the scattering material range from about 10 nm to about 400nm.

Although the lighting apparatus or the lamp 36 shown in FIG. 5 has astraight housing 38, other housing shapes may be used. For example, acompact fluorescent lamp may have a housing 38 that has one or morebends or is in a spiral shape, with electrical supply pins 48 that aredisposed at one end of the lamp 36.

By assigning appropriate spectral weights for each phosphor, one cancreate spectral blends to cover the relevant portions of color space forwhite lamps. Specific examples of this are shown below. For variousdesired CCT's, CRT's and color points, one can determine the appropriateamounts of each phosphor to include in the blend. Thus, one cancustomize phosphor blends to produce almost any CCT or color point, withcorresponding high CRI. Of course, the color of each phosphor will bedependent upon its exact composition (for example relative amounts ofBa, Ca, Sr, as well as Eu in nitride phosphor), which can change thecolor of the phosphor to a degree where it may have to be renamed.However, determining the changes in the spectral weight to produce thesame or similar characteristic lighting device necessitated by suchvariations is trivial and can be accomplished by one skilled in the artusing various methodologies, such as design of experiment (DOE) or otherstrategies.

By use of the present invention, particularly the blends described inherein, lamps can be provided having high luminosity and general CRIvalues greater than about 80, for a low range of color temperatures ofinterest (2500 K to 4000 K) for general illumination. In some blends,the CRI values approach the theoretical maximum of 100. In addition, theR₉ value for these blends can exceed about 90 and approach thetheoretical maximum as well. Table 1 and Table 2 show luminosity, CRIvalues and R₉ values of various blends at CCT values 2700K and 3000K,respectively.

EXAMPLES

The examples that follow are merely illustrative, and should not beconstrued to be any sort of limitation on the scope of the claimedinvention.

Various phosphor compositions according to the formulations listed inTable 2, were manufactured. The emission spectra of individual phosphorswere obtained, and used in calculations to predict emission spectra forvarious blends presented in Table 3. Further, the calculations alsoincluded any visible light emitted by a light source. FIGS. 6 and 7 showthe predicted emission spectra of the examples 1 and 2 of the blends inTable 3. The predicted amount of each phosphor based on spectral weightis shown in the Table 4 along with the spectral contribution of theemissions from the light sources, for example blue LEDs having peakwavelengths of 430 nm, 440 nm and 450 nm. Further, the spectralcharacteristics calculated from the predicted spectra for these blendsare also presented in Table 4. FIGS. 6 and 7 correspond to the blendexamples No. 4 and 3, respectively, of Table 4. Advantageously, theseblends generate white light having high luminosity, a high CRI value anda low CCT that can be tuned between 2500K and 3000K.

TABLE 2 Formulas of example phosphors used in the phosphor blend NameFormula CaSiG (Ca_(0.97)Ce_(0.03))₃Sc₂Si₃O₁₂ PFS K₂[SiF₆]:Mn⁴⁺ YAGY₃Al₅O₁₂:Ce³⁺ C-BASIN Ba_(1.538)Ca_(0.4)Eu_(0.06)Ce_(0.002)Si₅N₈ YONBa₄Si₉O₄N₁₂:Eu²⁺ SASOF(Sr_(0.895)Ca_(0.1)Ce_(0.005))₃Al_(0.6)Si_(0.4)O_(4.4)F_(0.6)

TABLE 3 Examples of phosphor blend produced Example. Phosphor blendExample 1 CaSiG/YAG/PFS Example 2 CaSiG/YON/PFS Example 3CaSiG/CBASIN/PFS Example 4 CaSiG/SASOF/PFS/YAG

TABLE 4 Wavelength Spectral of LED weight of Spectral Spectral SpectralSpectral Spectral Spectral Lumenosity emission LED weight weight weightweight of weight of weight of (lumen/ S. No. CCT (nm) emission of YAG ofPFS of YON CaSiG CBASIN SASOF watt) CRI R9 1 2700K 430 0.099 0.499 0.2950.106 320 85.9 90.7 2 440 0.0805 0.527 0.297 0.0945 328 87.6 92.4 3 4500.0777 0.552 0.294 0.0753 330 90.1 93.6 4 440 0.0714 0.308 0.25 0.37 32894.2 94.8 5 450 0.0899 0.273 0.232 0.404 330 95.8 96.9 6 430 0.099 0.4610.294 0.094 0.05 320 85.9 90.9 7 440 0.0805 0.49 0.297 0.826 0.049 32887.6 92.5 8 3000K 440 0.0921 0.278 0.2137 0.416 328 92.7 97.7 9 4300.122 0.442 0.265 0.169 319 85.1 87.7 10 440 0.099 0.475 0.267 0.157 32887.1 89.7 11 450 0.099 0.508 0.262 0.129 330 90.1 91.1 12 430 0.1 0.040.34 0.58 278 94 93 13 440 0.08 0.04 0.34 0.54 283 96 94 14 450 0.070.03 0.34 0.56 284 98 93

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A phosphor material comprising a blend of: a first phosphorcomprising a composition having a general formula ofRE_(2−y)M_(1+y)A_(2−y)Sc_(y)Si_(n-w)Ge_(w)O_(12+δ):Ce³⁺, wherein REcomprises a lanthanide ion or Y³⁺, M comprises Mg, Ca, Sr or Ba, Acomprises Mg or Zn; and 0≦y≦2, 2.5≦n≦3.5, 0≦w≦1, and −1.5≦δ≦1.5, asecond phosphor comprising a complex fluoride doped with manganese(Mn⁴⁺), and a third phosphor comprising a phosphor composition having anemission peak in a range from about 520 nm to about 680 nm.
 2. Thephosphor material of claim 1, wherein the first phosphor comprises acomposition of general formula (Ca_(1−z)Ce_(z))₃Sc₂Si_(n-w)Ge_(w)O₁₂,where 0<z≦0.3.
 3. The phosphor material of claim 1, wherein the secondphosphor comprises a general formula A₂[MF₆]:Mn⁴⁺, wherein A comprisesNa, K, Rb, Cs, NH₄, or a combination thereof; and M comprises Si, Ti,Zr, Mn, or a combination thereof.
 4. The phosphor material of claim 1,wherein the third phosphor comprises a garnet, a nitride, an oxynitride,or a combination thereof.
 5. The phosphor material of claim 4, whereinthe third phosphor comprises a garnet of general formula (A,Ce)₃M_(5−a)O_(12−3/2a), wherein 0≦a≦0.5, A comprises Y, Gd, Tb, La, Sm,Pr, Lu, or a combination thereof; and M comprises Sc, Al, Ga. Or acombination thereof.
 6. The phosphor material of claim 4, wherein thethird phosphor comprises a nitride of general formula (A,Eu)_(x)Si_(y)N_(z), wherein 2x+3y=4z, and A comprises Ba, Ca, Sr, or acombination thereof.
 7. The phosphor material of claim 6, wherein thethird phosphor comprises A₂Si₅N₈:Eu²⁺, Ce²⁺ wherein A comprises Ba, Ca,Sr, or a combination thereof.
 8. The phosphor material of claim 4,wherein the third phosphor comprises an oxynitride of a general formulaA_(p)B_(q)O_(r)N_(s):R, where A comprises barium, B comprises silicon,and R comprises europium; and 2<p<6, 8<q<10, 0.1<r<6, 10<s<15.
 9. Alighting apparatus comprising: a light source capable of emittingradiation in a range from about 400 nanometers to about 480 nanometers;and a phosphor material radiationally coupled to the light source, thephosphor material comprising a blend of: a first phosphor comprising acomposition having a general formula ofRE_(2−y)M_(1+y)A_(2−y)Sc_(y)Ge_(w)O_(12+δ):Ce³⁺ wherein RE is selectedfrom a lanthanide ion or Y³⁺, where M is selected from Mg, Ca, Sr or Ba,A is selected from Mg or Zn and where 0≦y≦2, 2.5≦n≦3.5, 0≦w≦1, and−1.5≦δ≦1.5, a second phosphor comprising a complex fluoride doped withmanganese (Mn⁴⁺), and a third phosphor comprising a phosphor compositionhaving an emission peak in a range from about 520 nm to about 680 nm.10. The lighting apparatus of claim 9, wherein the light sourcecomprises a light emitting device (LED).